What Happens If My Dog Tests Positive for Heartworm?

As part of our canine patients’ annual wellness care, our veterinarians recommend having pups tested for heartworm infection each year in order to prescribe heartworm prevention to be used over the mosquito season (June till November).

The reason our veterinarians send these preventive medications?

Grounded or unfounded heartworm disease in dogs explanation from the american heartworm society

(Click the image to make it larger)

What happens when a dog tests positive?
After a dog receives a positive result on the heartworm antigen screening test, further testing is required to confirm actual heartworm infection.

These tests include additional blood collection with the samples subjected to any of the following analyses:

  • A different manufacturer’s heartworm antigen test
  • Recovering microfilariae (heartworm larvae) circulating in the bloodstream
  • Complete Blood Count (CBC)
  • Chemistries to assess organ function (liver, kidneys)

Other tests include chest x-rays or urinalysis depending on the dog’s symptoms. Most dogs with the early infection do not display any symptoms.

As the disease progresses, the heartworm infected dog may show any of these signs:

  • cough
  • exercise intolerance
  • rapid breathing
  • fluid in the abdomen
  • pale mucous membranes with a blue-coloured tinge
  • incoordination
  • heart murmur
  • rapid heartbeat

Your veterinarian will consider all of your pet’s symptoms when combined with a positive antigen test result. Because of the risks involved in heartworm treatment, the doctors must be certain of their diagnosis. In a subsequent blog, we will be presenting the details of heartworm treatment in diagnosed dogs.

If you have any questions or concerns about heartworm disease, please contact us! We are happy to help.


  1. American Heartworm Society. (2018). Heartworm Basics. Retrieved from
  2. Dryden, M. W. (2017). Canine Heartworm Antigen Tests. Retrieved from
  3. VetStreet Inc. (2014). Heartworm Disease in Dogs. Retrieved from:

Written by: Seneca Animal Clinic



Senior dog giving a high five to a human hand

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Last updated: December 16, 2020

Dear Clients,

Thank you for choosing Seneca Animal Clinic for your pets' veterinary needs. As we continue to adjust to the "new normal," we have implemented new protocols to keep you and our team safe.

It is still preferred that you stay in your vehicle while we bring your pet in for their appointment. However, as of August 14, 2020, we will be allowing one client to accompany their pet during their visit for urgent, new puppy/kitten, or euthanasia appointments.

Should you choose to come in with your pet, we kindly ask that you comply with the following protocols:

  • Our doors will remain locked. Please call us at 416.494.1109 upon your arrival.
  • Face coverings must be worn to enter the clinic.
  • Physical distance with staff and other clients while inside the building.
  • Use hand santizing station upon entry.
  • Continue the use of credit cards as the preferred payment method.
  • Continue with curbside pickup of food and medication (unless you have used our online store and are having your order delivered directly to your home). To place an order through our online store, visit our website and click on "Online Store".
  • If you wish to wait in your vehicle during the appointment, when you arrive, please remain outside the hospital and use your cell phone to call us. We will take a history of your pet's health and discuss any concerns. A staff member will then meet you outside to bring your pet into the hospital for an examination. The Veterinarian will call you to discuss the recommended treatment plan. After your appointment, a staff member will return your pet to you outside, and take care of any needed medications and payment.

    If you wish to connect with a veterinarian via message, phone or video, visit our website and follow the "Online Consultation" link.


    Have you welcomed a new furry family member to your home? We’d love to meet them! Visit our Must Know New Pet Owner Information page for useful resources and helpful recommendations for new pet owners.


    We are OPEN with the following hours:

    - Monday & Tuesday: 8:00 am - 6:30 pm
    - Wednesday: 8:00 am - 6:00 pm
    - Thursday: 8:00 am - 6:30 pm
    - Friday: 8:00 am - 6:00 pm
    - Saturday: 9:00 am - 1:00 pm
    - Sunday: CLOSED

    Thank you for your patience and understanding and we look forward to seeing you and your furry family members again!

    - Your dedicated team at Seneca Animal Clinic